Centrifugal pump with reinforced plastic impeller wheel

ABSTRACT

A centrifugal pump has a housing forming a chamber having intake and output ports and a plastic lining in the chamber An impeller wheel in the chamber is formed by a hub rotatable about an axis, a rear disk projecting radially from the hub, a front disk projecting radially from the hub and offset axially from the rear disk, and radial vanes extending axially between the disks. The hub, disks, and vanes are formed of a high-strength material such as metal and carries a coating on outer surfaces of the hub, disks, and vanes of a plastic of lower strength than the material.

FIELD OF THE INVENTION

The present invention relates to a centrifugal pump. More particularly this invention concerns a reinforced plastic impeller wheel for such a pump.

BACKGROUND OF THE INVENTION

A centrifugal pump normally has a housing forming a chamber holding an impeller wheel and has intake and output ports, with the chamber and the intake and output port being lined with protective plastic and the impeller wheel consisting mainly of plastic, and with the rear disk of the impeller wheel that is facing away from the chamber intake having an inner support core.

A centrifugal pump with inner plastic lining and a plastic impeller wheel with a rear wheel that is reinforced by means of a metal insert is known from EP 0 797 736. In this known pump, the stability of the plastic impeller wheel is improved. Nevertheless, the impeller wheel is not able to handle very high hydraulic outputs. The dynamic and static loads of the impeller wheel under pressure, temperature, and high speed can exceed the yield strength of the plastic and cause the impeller wheel to break.

OBJECTS OF THE INVENTION

It is therefore an object of the present invention to provide an improved centrifugal pump.

Another object is the provision of such an improved centrifugal pump that overcomes the above-given disadvantages, in particular that can transfer very high hydraulic outputs.

SUMMARY OF THE INVENTION

A centrifugal pump has according to the invention a housing forming a chamber having intake and output ports and a plastic lining in the chamber. An impeller wheel in the chamber is formed by a hub rotatable about an axis, a rear disk projecting radially from the hub, a front disk projecting radially from the hub and offset axially from the rear disk, and radial vanes extending axially between the disks. The hub, disks, and vanes are formed of a high-strength material such as metal and carries a coating on outer surfaces of the hub, disks, and vanes of a plastic of lower strength than the material.

Thus according to the invention the front disk and the impeller wheel vanes, which connect the rear disk and the front disk to one another, each have an inner support core made of metal or of a plastic having a higher strength value than that of the plastic coating.

Such a solid core made of metal or of a high-strength plastic provides reinforcing support from the shaft-hub connection of the pump shaft to the rear disk to the pump vanes and to the front disk, thus enabling high hydraulic loads to be transferred and high speeds to be reached. All hydraulic forces are introduced into the support core via the shortest path, thereby relieving the plastic of the impeller wheel. Due to the significant increase in transmitted power, the limits of use for plastic-lined centrifugal pumps are increased substantially in terms of pump head, delivery rate, and temperature. The support core of the front disk is connected cohesively or positively to the support core of the rear disk via the support cores of the impeller wheel vanes.

Preferably, it is proposed that the support cores of the rear disk, the front disk, and the impeller wheel vanes together form a supporting framework. In that case, the supporting framework is integrally formed.

An optimal force path is achieved if the support cores reproduce the contours of the front disk, rear disk, and vanes partially or completely true to form. Thus the plastic coating is of uniform thickness so the outer surface of the coating is identical to but larger than the outer surface of the core parts.

Robust anchorage of the plastic of the impeller wheel to the support cores is achieved if the support cores have clamping holes and/or clamping grooves that are filled by the plastic of the impeller wheel.

It is also proposed that the inner core of the rear disk be connected positively or non-positively to the pump drive shaft.

BRIEF DESCRIPTION OF THE DRAWING

The above and other objects, features, and advantages will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial section through an impeller wheel according to the invention; and

FIG. 2 is a section through the impeller wheel according to the invention at the level of its vanes.

SPECIFIC DESCRIPTION OF THE INVENTION

A centrifugal pump has an unillustrated two-part housing shown in broken lines at 6 and joined at a plane 9 that extends through a chamber 10, so that the inner walls of the chamber 10 and of intake and output ports 11 and 12 can be provided with little effort with a lining 13 of a plastic that protects the inner walls of both the chamber and the ports 11 and 12. The housing 6 is made of metal or of a hard plastic composite. A fully fluorinated, partially fluorinated, or non-fluorinated plastic is used as the plastic of the lining 13 in order to obtain high-quality corrosion or purity protection of the pressure- and power-transmitting pump parts.

An impeller wheel 1 enclosed in the plastic-lined chamber 10 has a hub 8 from which a circular rear disk 2 extends radially. The hub 8 is formed with a blind normally threaded bore 7 that receives one end of a shaft 14 of an electric motor 15 or magnetic coupling. Furthermore, the impeller wheel 1 has a front annular front disk 3 that is of frustoconical shape and forms a central annular suction opening 4 aligned with the intake port 4. The plate 3 is connected by radially extending but arcuate vanes 5 to the rear disk 2 so that rotation about an axis A of the shaft 15 draws a fluid (normally a liquid) radially inward through the ports 11 and 4 and expels it radially outward between the vanes 5 from the port 12.

The hub 8, rear disk 2, front disk 3, and vanes 5 are unitarily formed as a core from cast metal or from a high-strength plastic or plastic composite of greater strength than the liner 13 of the pump chamber 10. The one-piece structure formed by this hub 8, disk 2, disk 3, and vanes 5 is covered on all outer surfaces by a coating or layer 16 of a plastic of less strength and/or hardness than that forming the hub 8, disks 2 and 3, and vanes 5, for instance the same as forms the lining 13.

In one embodiment, the parts forming the hub 8, disks 2 and 3, and the vanes 5 are separate but integrally connected together. Preferably, however, all of these parts are made of the same metal or of the same high-strength plastic and are connected to each other cohesively or positively, so that the hub 6, disks 2 and 3, and vanes 5 are unitarily interconnected and thus together form a supporting, one-piece framework made of metal or high-strength plastic that is surrounded, particularly extrusion-coated, by the plastic coating 16 of the impeller wheel 1 or a fully or partially fluorinated plastic such as perfluoroalkoxy alkane (PFA) or polytetrafluoroethylene (PFAPVDF) is preferably used. The coating 16 is of uniform thickness and closely and uniformly fits to the contours of the hub 8, disks 2 and 3 and vanes 5 partially or completely true to form.

In order to achieve an intimate bond between the outer plastic coating 16 of the impeller wheel 1 and the cores, each of the parts 8, 2, 3, and 5 of the wheel 1 has mounting bores and/or clamping grooves into which engages the plastic of the coating 16 of the impeller wheel 1. One such grip formation is shown as a plastic-filled hole 17 through the rear disk 2. 

We claim:
 1. A centrifugal pump comprising: a housing forming a chamber having intake and output ports; a plastic lining in the chamber; and an impeller wheel in the chamber and formed by a hub rotatable about an axis, a rear disk projecting radially from the hub, a front disk projecting radially from the hub and offset axially from the rear disk; radial vanes extending axially between the disks, the hub, disks, and vanes being formed of a high-strength material; and a coating on outer surfaces of the hub, disks, and vanes of a plastic of lower strength than the material.
 2. The centrifugal pump defined in claim 1, wherein the front disk is cohesively or positively connected to the rear disk by the vanes.
 3. The centrifugal pump defined in claim 2, wherein the hub, disks, and vanes are integral.
 4. The centrifugal pump defined in claim 2, wherein the hub, disks, and vanes are unitary.
 5. The centrifugal pump defined in claim 3, wherein the hub, disks, and vanes are unitarily formed of cast metal.
 6. The centrifugal pump defined in claim 1, wherein the plastic coating on the hub, disks, and vanes, is of uniform thickness.
 7. The centrifugal pump defined in claim 1 wherein the hub, disks, and vanes have surface formations interfitting with the plastic coating.
 8. The centrifugal pump defined in claim 7 wherein the formations are grooves or holes.
 9. The centrifugal pump defined in claim 1, wherein the hub is configured to be rotated by a drive shaft.
 10. The centrifugal pump defined in claim 1, wherein the lining and the coating are of the same plastic. 